1. Field of the Invention
The present invention relates to a high-frequency circuit device such as a wave guide or a resonator, having two parallel planar conductors, and a communication apparatus employing such a high-frequency circuit device.
2. Description of the Related Art
A variety of transmission lines may be employed in apparatuses operating in the micro-wave band and the millimeter-wave band. The following transmission lines are typically available: (i) a grounded coplanar line composed of a dielectric plate with one side generally coated with a ground electrode and the other side having a coplanar line thereon; (ii) a grounded slot line composed of a dielectric plate with one side coated with a ground electrode and the other side having a slot; and (iii) a planar dielectric line composed of a dielectric plate with both sides having slots.
Each of the above transmission lines usually have two parallel planar conductors. When an electromagnetic field is disturbed by input and output sections and bend sections of the transmission line, a spurious mode wave (also simply referred to as a xe2x80x9cspurious modexe2x80x9d), such as a parallel-plate mode wave, is induced and travels between the two parallel planar conductors. For this reason, the leaky spurious mode waves interfere with each other between adjacent lines, presenting the problem of leakage signals.
FIG. 38 illustrates the main transmission mode of a grounded coplanar line and the distribution of a parallel-plate mode electromagnetic field which is generated along with it. As shown, the underside of a dielectric plate 20 is generally coated with an electrode 21 and the top surface of the dielectric plate 20 has a strip conductor 19 and an electrode 22. The electrodes 21 and 22 serve as ground electrodes, and the grounded coplanar line is thus composed of electrodes 21 and 22, the dielectric plate 20 and the strip conductor 19. In such a grounded coplanar line, the electromagnetic field may be disturbed at its edges such that an electric field is established in a direction perpendicular to the electrodes 21 and 22, and a parallel-plate mode electromagnetic field occurs as shown. Solid lines with arrow heads represent the electric field, broken lines represent the magnetic field, and two-dot chain lines represent the distribution of currents.
To control the propagation of such an unwanted mode wave, through holes are conventionally provided along both sides of a transmission line at a pitch shorter than the wavelength of a transmission mode wave, thereby connecting top and bottom electrodes arranged on the top and bottom faces of a dielectric plate.
The through holes, arranged along the direction of propagation for connecting the top and bottom electrodes, serves as a wall (hereinafter referred to as a xe2x80x9celectric barrierxe2x80x9d), blocking the propagation of the parallel-plate mode wave. However, in a high frequency region, such as the millimeter-wave band, the dielectric plate must be thin to control the generation of harmonic mode waves, and the intervals between the through holes must be extremely short. This involves high processing accuracy in the manufacture of the circuit device.
When no through holes are arranged in the dielectric plate, the dielectric plate having electrodes thereon are entirely housed in a cutoff wave guide. In such a case, however, the dimensions of the cutoff wave guide must be equal to or smaller than half the guide wavelength, and the dimensional requirements of the wave guide become severer.
A portion of the electrode where the spurious mode wave leaks can be partially cut away to form a wall (hereinafter referred to as a xe2x80x9cmagnetic wallxe2x80x9d) to block the propagation of the spurious mode wave. This arrangement poses a new problem because the cutout portion of the electrode functions somewhat as a resonator.
Accordingly, it is an object of the present invention to provide a high-frequency circuit device which blocks the propagation of the spurious mode waves such as parallel-plate mode waves, while being free from the above-described problem associated with the electric wall of through holes and the magnetic wall of the cutout portion of an electrode.
When the electromagnetic field is disturbed on a strip conductor and electrodes are arranged on both sides of the strip conductor in a grounded coplanar line, spurious mode electromagnetic waves, such as a parallel mode wave, travel between the two parallel electrodes and reach the boundary of an electrode pattern. Since the configuration of the transmission line changes beyond the boundary, a portion of the electromagnetic wave is reflected from the boundary. The electromagnetic wave is disturbed at the discontinuity section of the electrode pattern, as the transmission line, and is converted into a mode which is transmitted through the transmission line configuration. Thus, a mode conversion is performed. The present invention takes advantage of this operation. A circuit is arranged to reflect a mode into which the spurious mode such as the parallel-plate mode is converted, thereby blocking the propagation of the spurious mode waves beyond the circuit.
A high-frequency circuit device of the present invention includes at least two planar conductors and a circuit for exciting an electromagnetic wave between the two planar conductors. A spurious mode propagation blocking circuit including a conductor pattern which blocks the propagation of a spurious mode wave by being coupled with the spurious mode wave that travels between the two planar conductors is arranged in at least one of the two planar conductors. The spurious mode propagation blocking circuit is coupled with the spurious mode wave traveling between the two planar conductors, thereby blocking the propagation of the spurious mode wave. Since the spurious mode propagation blocking circuit is formed in the planar conductor by simply patterning the electrode, any problems, such as the ones associated with the formation of the through holes in the conventional art, are not presented.
The conductor pattern of the spurious mode propagation blocking circuit preferably includes a plurality of micro-strip lines spaced apart at a pitch shorter than the wavelength of the electromagnetic wave.
In the high-frequency circuit device of the present invention, the micro-strip line of the spurious mode propagation blocking circuit is preferably a serial connection in which a high-impedance line and a low-impedance line are alternately connected in series. The spurious mode, such the parallel-plate mode, is converted into another mode at the micro-strip line and the resulting signal at a predetermined frequency is reflected. The propagation of the spurious mode wave is thus blocked.
In the high-frequency circuit of the present invention, a plurality of micro-strip lines are preferably arranged with their terminals opened. The spurious mode wave is thus converted into a micro-strip mode wave, which is then reflected from the open terminal. The spurious mode wave is thus blocked.
The conductor pattern of the spurious mode propagation blocking circuit preferably includes a plurality of basic patterns which are arranged at a pitch shorter than the wavelength of the electromagnetic wave, with the line of one basic pattern being connected to the line of the adjacent basic pattern, and wherein the basic pattern includes a polygonal or circular electrode for creating a capacitance with the other planar conductor different from one planar conductor forming the basic patterns and a plurality of lines connected to the electrode. Even when the spurious mode waves are reflected in a multiple fashion, the circuit device blocks the spurious mode waves, not only in a direction perpendicular to the direction of propagation of the spurious mode wave but also in a direction parallel to or in an acute (or obtuse) direction with respect to the direction of propagation of the spurious mode.
Preferably, the electrode which creates a capacitance with the other planar conductor different from the one planar conductor forming the basic patterns, is arranged at a junction position of the adjacent basic patterns. By choosing a proper circuit constant, a large blocking capability is provided in the blocking of the spurious mode wave.
Preferably, from among a plurality of lines connected to the electrode, no two lines are aligned in a line with each other in orientation or in junction position. In this way, the signal from one line (port) is equally distributed among other lines (ports), thereby increasing the transmission loss between two ports.
Preferably, the conductor pattern of the spurious mode propagation blocking circuit includes a plurality of basic patterns, each pattern being a two-terminal pair circuit composed of three strip lines, one central line and two end lines, connected in series, and wherein the coupling between the end lines is set to be stronger than the coupling between the central line and each of the two end lines. The micro-strip mode wave, into which the spurious mode is converted, is preferably sufficiently reflected (even when a low-dielectric-constant dielectric plate having an impedance which does not change greatly with the line width of the strip line varying, or a thick dielectric plate is used).
Preferably, the circuit for exciting the electromagnetic wave is a transmission line, and the spurious mode propagation blocking circuit is arranged between the transmission line and another transmission line or a resonator. This arrangement prevents the interference of leaky waves between the adjacent transmission lines, and the interference of leaky waves between the transmission line and the resonator.
Preferably, the transmission line is a grounded coplanar line, a grounded slot line, a strip line, a planar dielectric line, or a dielectric line.
The circuit for exciting the electromagnetic wave is preferably a resonator and the spurious mode propagation blocking circuit is preferably arranged on the periphery of the resonator. This arrangement prevents the interference of leaky waves between the resonator and the other transmission line and between one resonator and the other resonator.
The resonator may be of a type which has non-conductive cutout portions, formed on parallel planar conductors and serving as a magnetic wall. The electromagnetic wave is confined between the cutout non-conductive portions. Alternatively, the resonator may be of a type which has electric walls formed on parallel planar conductors and the electromagnetic wave is confined between the non-conductive cutout portions.
A communication apparatus preferably includes a high-frequency circuit device in a signal transmission section or in a signal processing section.